Life Among Parasitic Animals AT 
the kind, is to invite as vehement a denial as though he were charged 
with the act of receiving stolen goods. The interest and surprise are 
even greater when I suggest to you that one-fourth of the faces here 
have these elongate, six- or eight-legged mites in the pores over the 
nose, at the side of the nose, and in the furrow between the lower lip 
and chin, if I may judge from a twenty-eight per cent and a thirty- 
three-and-one-third per cent infestation in two classes of my students 
in parasitology. 
The face mites are barely able to move about by means of their 
short, chubby legs. When not in the sebaceous secretion of the hair 
follicles, therefore, how do they migrate? How do they find a new 
host? More forceful than the question, ‘How might they spread from 
myself to others?” is the one, “How did they spread from others vo 
me?” The substance which one might press out of the skin as a “‘com- 
medone” or a “‘blackhead” is not either a worm or a mite, but in that 
material they may be found in numbers ranging from a single indi- 
vidual to several, if a person is infested. I have found as many as 
one hundred in a single follicle from a dog infested with follicular 
mange. It is possible to expel the mites by pressure or by friction 
applied to these regions of the face, and it is not beyond the realm 
of the possible that the friction, as of wiping the face with a towel, 
may serve to dislodge specimens from the pores, or to pick up others 
that were in the act of migrating from pore to pore over the surface 
of the face, and thus to my own face, if I chanced to use a towel pre- 
viously used by an infested person. 
A heavily chitinized cuticle, which covers the whole body of the 
face mite, makes it possible to withstand dessication, or even the effects, 
for several minutes, of a ten per cent solution of caustic potash, before 
it is killed. I have observed a mature specimen, while lying on its back 
in a ten per cent solution of potassium hydrate, to move its four pairs 
of legs with the rhythm that suggested the co-operative action of the 
members of a crew of an eight-oared boat. 
A brief reference to the parasitic worms will serve to indicate that 
the hazards of life are such that, in spite of the enormous number of 
eggs and young, the total number of adult forms does not increase 
markedly from year to year. It is estimated that Taenia saginata, the 
tapeworm which man may acquire by eating infested rare beef, is capable 
of producing one hundred and fifty million eggs in a single year; 
that a liver fluke produces one hundred thousand eggs in its lifetime; 
and so the numbers might be multiplied at length to indicate that 
these, and other parasites, must meet handicaps that do not occur in 
the life of larger animals with which we are more familiar. 
The intestinal worms, which by rare chance find their way into the 
digestive tract of any host, are plunged into digestive ferments that 
would digest materials like those of the parasite, and in fact this does 
occur if chance brings them into some animal with a more vigorous 
digestion, as, for example the introduction of hog lung-worms into the 
digestive tract of a rat, where a large number are digested. The ex- 
perimental work of Birge and Birge of the University of Illinois throws 
some light upon the question of the non-digestion of such forms as 
